Record-High Organic Device Performance enabled by Polymorphism in Organic Semiconductors

有机半导体薄膜加工方法的最新发展使非平衡晶型稳定下来，具有显著更好的电气设备性能。这些进展突出了控制多态以最大限度地提高给定材料性能的重要性。然而，到目前为止，还没有办法预测哪些材料可以预期多晶性，以及不同的多晶型可以提供什么样的电性能。可能的结果是，许多材料，无论是现有的还是尚未合成的，都已经或将被宣布在设备中表现不佳，仅仅是因为它们没有以一种产生(未知的)高性能多晶型薄膜的方式进行加工(S)。为了改善这种情况，我们建议建立一个理论框架来预测小分子有机半导体中的多态，并根据预测的电学性质对潜在的多态进行排序。作为补充，我们将使用一种特殊的印刷方法来检测和稳定印刷薄膜中可溶有机物质的多态，这将为有待开发的理论提供非常必要的实验基准和校准参考。各种实验工具将被用来精确地确定印刷薄膜中的分子堆积，从而为理论提供有价值的反馈。理论方法将通过考虑许多不同的晶型来建立分子结构和电性能之间的直接联系，而不是在使用传统沉积技术时通常遇到的热力学平衡的晶型。这种方法创造了一整套可能的结构实现，具有意想不到的更高的载流子迁移率，可能是某些分子的数量级。在实验部分，我们将检验这一新理论所作的预测，特别是那些它认为具有高技术相关性(高载流子迁移率)的预测。我们将使用现代沉积技术来引入沉积条件的可变性，这是实现这种多晶型所必需的。将对材料进行表征，并对电子设备进行分析并与理论进行比较。建议的面向设备的模拟框架将基于一组有限的结构开发，但具有普遍适用性，是一个战略工具，可能会引发大量新的高迁移率材料，否则这些材料将一直未被发现。这可以极大地改变进行材料分析和设计的方式，并应该催化从合成到器件测量的整个链的研究。

Recent developments in thin film processing methods for organic semiconductors have allowed the stabilization of non-equilibrium polymorphs with drastically better electrical device performance. These advances highlight the importance of controlling polymorphism to maximize the performance of a given material. However, so far there is no way to predict for which materials polymorphism can be expected and what electrical performance the different polymorphs can deliver. As a likely result, many materials, both existing and yet to be synthesized, have been or will be declared poorly performing in devices simply because they are not processed in a way that produces films of the (unknown) high-performance polymorph(s). In order to remedy this situation, we propose to develop a theoretical framework to predict polymorphism in small molecule organic semiconductors and to rank potential polymorphs based on their predicted electrical properties. In a complementary effort, we will employ a special printing method to detect and stabilize polymorphic forms of soluble organic materials in printed thin films, which will provide the very necessary experimental benchmarks and calibration references to the to-be-developed theory. Various experimental tools will be used to precisely determine the molecular packing in the printed films thus providing valuable feedback to theory.The theoretical approach will establish a direct link between molecular structure and electrical performance by considering many different polymorphs beyond the one in thermodynamic equilibrium that is usually encountered when employing conventional deposition techniques. The approach creates a whole set of possible structural realizations with expectedly higher carrier mobilities, possibly by orders of magnitude for some of the molecules. In the experimental part, we will test the predictions made by this new theory, especially those that it suggests to be of high technological relevance (high charge carrier mobility). We will use modern deposition techniques to introduce the variability in deposition conditions which is necessary to realize such polymorphs. Materials will be characterized and electronic devices will be analyzed and compared to theory.The proposed device-oriented simulation framework will be developed based on a restricted set of structures but is generally applicable and is a strategic tool that could spark a vast amount of novel high-mobility materials that would otherwise remain undiscovered. This could significantly transform the way of performing material analysis and design and should catalyze the research along the whole chain from synthesis to device measurements.